Martin and Sylvia's family are taking a trip to the coast of Maine!  And they are so excited.  Brother and sister are initially disappointed when they see that their vacation on the ocean is situated on what looks like an empty basin of mud.  When friends explain that "the tide is out", the children have a chance to learn all about the amazing natural rhythm of "the tides".  They also learn about all sorts of tidal adventures that follow the ever-changing waters.